This invention relates to keyboards and in particular to solid state keyboards.
Keyboards using magnetically responsive Hall Effect generators to effect solid state switching action are known in the prior art. One such keyboard is described by Dalmasso (U.S. Pat. No. 3,611,358). Attached to each keystem of the Dalmasso keyboard is a two-pole magnet which moves with the key in rectilinear fashion relative to a stationary Hall Effect generator which senses a change in the intensity of the magnetic flux as the magnet approaches and recedes. A similar keyboard is described by Maupin et al (U.S. Pat. No. 3,596,114) in which a keyswitch moves a two-pole magnet supported thereby in rectilinear fashion relative to a stationary Hall Effect generator.
Other related references are Turja (U.S. Pat. No. 3,449,517) which shows a keyboard with a Hall Effect generator moved relative to a stationary magnet, and Semmelman (U.S. Pat. No. 2,774,890) which shows the input and output terminals of a Hall Effect generator asymmetrically positioned.
Keyswitches used in prior art keyboards have permanent magnets attached to a keystem, plunger or other means for moving the magnets in rectilinear fashion in response to manipulation of the keyswitches. Because magnetic material such as barium ferrite cannot itself be molded, a binder such as nylon is required in which to suspend the barium ferrite particles and to provide a workable substance. In the preferred embodiment, a lubricating silicone is also added.
Offset voltage associated with Hall Effect generators reduces the sensitivity of Hall Effect keyboards. The greater the offset voltage, the greater intensity of magnetic flux through the generator that is needed to effect switching action. Furthermore, differences in offset voltages among various Hall Effect generators in a keyboard necessitate "tuning" or matching of particular magnets to be used with particular Hall Effect generators with different offset voltages. This increases the complexity and expense of assembling the keyboard. Finally, the two-pole magnet arrangement used in prior art keyboards does not provide the positive switching desired because the Hall Effect generators are exposed to linear changes in the magnetic field as the magnets move in response to actuation of their respective keyswitches rather than an abrupt, positive change in magnetic field. Thus, on-off switching points are not well-controlled.